Method of repairing cracks

ABSTRACT

The invention discloses a method of repairing cracks, which is characterized in that, in injecting a repairing agent such as resin or the like into cracks occurring in an object to be repaired such as concrete, a masonry joint or the like, injection pressure of the repairing agent gradually increases after start-up of injection of the repairing agent and, further, the injection pressure is maintained substantially constant for a predetermined period of time after the injection pressure has reached a predetermined pressure, whereby the repairing agent is sufficiently spread into the cracks. Furthermore, the invention discloses a method of repairing cracks, in which the crack cavities are evacuated simultaneously with injection of the repairing agent, whereby the repairing agent is filled up in the cracks further efficiently.

FIELD OF THE INVENTION

This invention relates to a method of injecting a repairing agent intocracks occurring in concrete or a base rock, a masonry joint of brickmasonry and rock masonry, or the like, to repair the cracks.

BACKGROUND ART

As known well, concrete is a composite material which utilizes the factthat, when water is added to gravel, sand and cement and is kneadedtogether with the latter, the water and the cement are hardened underhydration reaction. Since the concrete is long in durability, and ishigh in strength and, further, is low in cost, the concrete is widelyused in various fields. Particularly, the concrete is a material whichis essential for buildings and civil engineering construction. However,the concrete alone is extremely low in bending strength and tensilestrength, and cannot sufficiently stand up against a bending force and atensile force. In order to strengthen or reinforce this disadvantage, amethod has been invented which utilizes concrete reinforced with steelproducts. It is the existing condition that the compound of the concreteand the steel products is widely utilized for many buildings asreinforced concrete or steel concrete.

It cannot be avoided that, as a basic property of the concrete dryshrinkage occurs due to evaporation of excess mixed water duringhardening, and many minute cracks are generated at various locations.The cracks per se are elucidated in view of structural mechanics, to beof no problem. However, secondary influences caused by the cracks, forexample, leaking of rain in a concrete building, corrosion or erosion ofreinforcement due to leaking water from cracks, reduction in structuralstrength caused by the corrosion, and the like, are so serious as todown grade a material value of the concrete. Accordingly, when cracksoccur in the concrete or the reinforced concrete, it is essential torepair the cracks. Conventionally, the following repairing methods areemployed.

Repairing methods normally practiced conventionally are divided broadlyinto two categories, depending upon the size or dimension of the cracks.

The first method is one which is employed in the case where crack widthis relatively wide such as those above a value of the order of 1 mm, anda repairing material can easily be poured into the cracks. In themethod, a concrete surface is cut out in the form of a letter x or xalong the cracks, a repairing agent such as cement milk, mortar or thelike is poured into the cracks by the use of a simple appliance and,subsequently, the cut-out portions are filled up by cement mortar orresin mortar, to repair the cracks.

The second method is one in which various injection appliances are usedto inject, under pressure, a repairing agent such as resin or the likeinto cracks. The method is utilized in the case where the crack width isof the order of 1 mm or less, and the repairing material like onedescribed above cannot easily be poured into the cracks. In this case,the narrower the crack width, and the deeper the depths of the cracks,the larger the injection resistance. Accordingly, various appliances areused which are so contrived that elastic springs, hydraulic pressure orpneumatic pressure, or rubber elasticity is utilized to produce apredetermined injection pressure. Various examples of the appliances areshown in FIGS. 12 through 15.

An appliance illustrated in FIG. 12 is one in which an elastic force ofa rubber tube is utilized to produce injection pressure. The arrangementis such that a resin (a repairing agent) 2 is forced into a rubber tube1 by a grease pump to inflate the rubber tube 1 like a balloon, and acontractile force of the rubber tube 1 causes the resin 2 to be injectedinto the cracks.

An appliance illustrated in FIG. 13 is one which is arranged such that aresin is put in a cylinder 3 in the form of an injector or syringe madeof a plastic material, and a contractile force of rubber straps 4 and 4causes a piston to be pushed into the cylinder to inject the resin.

An appliance illustrated in FIG. 14 is one which is arranged such that apressure tank 6 having a check valve 5 is mounted on cracks, resin 2 isinjected into the pressure tank 6 by a grease pump 7 to increase orraise air pressure within the pressure tank 6, and the air pressurecauses the resin 2 to be injected into the cracks.

An appliance illustrated in FIG. 15 is one which is arranged such thatan elastic spring 10 is arranged at a rear portion of an internalpressurizing plug 9 of a cylinder 8 in the form of a syringe, a lever 11connected to the internal pressurizing plug 9 is pulled back end to drawthe resin 2 into the cylinder 8 and, simultaneously, the elastic spring10 is contracted, and an elastic repelling force of the elastic spring10 causes the pressurizing plug 9 to be pushed forwardly to inject theresin 2 into the cracks.

In addition to the above-described appliances, there is such anarrangement or the like that a capsule having put a resin is placed in apressure vessel or container, is set, and compressed air is deliveredinto the pressure container by a compressor, thereby compressing thecapsule to push the resin out thereof.

As described above, in the case where the crack width is large, it ispossible to relatively easily pour the repairing agent such as thecement milk or mortar into the cracks and, thus, it is possible toeasily repair the cracks. Generally, however, the cracks occurring inthe concrete include many small ones equal to or less than 1 mm. Onoccasion, there are minute cracks of the order of a few micrometers.Accordingly, it is not necessarily easy to completely repair the minutecracks.

That is, in that case, the various appliances described above are usedto inject the resin into the cracks. In order to practice completeinjection, however, injection pressure larger than the injectionresistance must be maintained for a long period of time. Further, sincethe injection resistance increases in proportion to the length of thecracks and the depth thereof, it is required that the injection pressureincreases gradually. This is apparent from the Bernoulli theorem.

For the conventional method in which the above-described appliances areemployed to inject the resin into the cracks, it is impossible tomaintain of the injection pressure for long period of time and toincrease the injection pressure gradually afterwards. Accordingly, it isimpossible for any of the above-described appliances to sufficientlyinject the resin into the cracks.

That is, in view of the mechanism for generating the injection pressure,all of the above-described appliances are characterized in that theinjection pressure is maximum at the initiation point of injection,subsequently, is gradually reduced and, at last, approaches 0 (zero).Thus, it is impossible to retain the injection pressure necessary forthe injection. For example, in the appliance illustrated in FIG. 12, thepressure within the rubber tube is maximum before the start-up ofinjection. When the injection starts and the quantity of the resin 2within the rubber tube 1 decreases, the injection pressure is attenuatedrapidly. This is the behavior which is against the injection theory inwhich the injection pressure must gradually increase. For the use ofsuch appliance, it is impossible to practice complete injection. For theappliances illustrated in FIGS. 13 through 15, the circumstances areidentical with the above ones.

The behavior of the conventional various appliances will be described infurther detail with reference to FIG. 16. The abscissa in FIG. 16indicates "a lapse of time from the start-up of injection or aninjection length", while the ordinate indicates "the injection pressureof the appliance" and "the requisite injection pressure". The referencenumeral 20 denotes a linear variation of the injection pressure in theconventional appliance, and the reference numeral 21 denotes a lineindicating a varying condition of requisite injection pressure which isrequired for practicing complete injection.

In the figure, in the conventional appliance, the injection pressure ismaximum at the point of time of injection start-up and, subsequently, isgradually attenuated. It is indicated, however, that the requisiteinjection pressure must gradually increase, conversely. It will be seenthat, in spite of the fact that the injection pressure indicated by apoint b is required at a point b', the use of the conventional applianceenables only injection pressure of almost 0 (zero) to be produced at thepoint b'. Further, the total energy required for practicing completeinjection is indicated by an area enclosed by O-b-b', while the totalenergy generated by the conventional appliance is indicated by an areaenclosed encircled by c-b'-O. In the case where the maximum injectionpressure c of the appliance is equal to the requisite maximum injectionpressure b, the total energy required for complete injection and thetotal energy generated by the appliance become equal to each other.Since, however, the injection requirements and the appliancecapabilities are incompatible, half of the energy generated by theappliance is wastefully consumed. The energy used as the effectiveinjection energy is only the area enclosed by O-a-b'. Since the energyencircled by O-c-a is generated at a stage which is not required forinjection, not only the energy enclosed by O-c-a is not totally utilizedeffectively, but also bad effects are caused, such that the crack widthis widened or, the concrete at the loosened crack portion falls off, andso on.

In the case where the conventional appliance is used, the completeinjection cannot be practiced even if an appliance is used which cangenerate pressure equivalent to the injection pressure required forpracticing the complete injection. That is, even if an appliance of 4 Kgof the conventional system when the maximum injection pressure isrequired by 4 Kg, repair cannot be practiced with respect to cracks inwhich the maximum requisite injection pressure is 4 Kg. In order topractice complete injection by the conventional appliance, the lattermust be arranged such that the requisite injection pressure is producedat the final point in time. In the appliance, however, not only themaximum injection pressure becomes excessive at the time of injectionstart-up so that the bad influence like those described above occurs,but also the appliance must be large-sized in order to generate suchlarge injection pressure. Large-sizing of the appliance causes handlingproblems, and causes large danger to be attended with. Thus, theappliance is not practical.

Furthermore, in the case where the above-described conventionalappliances are used, it is possible to raise the injection pressure byaddition of hydraulic pressure or by addition of a quantity of air. Tothis end, however, intervention of man power will be required and theinjection operation becomes troublesome. This is also not practical.

In connection with the above, in FIG. 16, the varying condition of therequisite injection pressure is indicated in a straight line manner. Inpractice, however, the varying condition of the requisite injectionpressure does not necessarily become linear attendant upon a change inthe frictional resistance between the crack width and the periphery, andthe varying condition of the injection pressure generated by theappliance does not become linear depending upon the structure orconstruction of the appliance. In either case, however, such a conditioncannot be fulfilled that the maximum injection pressure is requiredimmediately after injection start-up. Further, it is out of the boundsof possibility that, in the conventional appliance, the injectionpressure becomes maximum at the final point in time.

Disadvantages of the repairing method, which utilizes the conventionalappliances, will be summarized below:

1. The generation behavior of the injection pressure is opposite to therequired condition of variation in pressure required for injection, andthis is illogical.

2. In order to retain the injection pressure constant to practicecomplete injection, intervention due to man power is always required sothat it is impossible to eliminate or reduce labor.

3. In order to produce high injection pressure, a complicated and largeappliance is required, and special skilled laborers are always required.

4. Since the injection pressure cannot be maintained for a long periodof time, it cannot be confirmed that injection becomes incomplete due toshortage or insufficiency of the injection pressure. In connection withthe above, the above is applicable not only to the case where cracksgenerated in the concrete are repaired, but also equally to the casewhere repair is made to cracks in a base rock, and to cracks occurringin stone or brick, or in a masonry joint of a concrete block building.

SUMMARY OF THE INVENTION

An object of the invention to provide a method capable of reasonably andcompletely practice repairing of cracks which occur in concrete, amasonry joint or the like.

The invention is characterized in that, in injecting a repairing agentsuch as a resin or the like into cracks occurring in an object to berepaired such as concrete, a masonry joint or the like, an injectionappliance is used which comprises a driving source made of ashape-memory alloy to inject the repairing agent into the cracks by ashape restoring force of the shape-memory alloy, whereby injectionpressure of the repairing agent into the cracks gradually increasesafter the injection has started, and from the time the injectionpressure reaches maximum, and the maximum injection pressure ismaintained for a predetermined period of time. It is desirable thatinjection of the repairing agent into the cracks by the injectionappliance is practiced while evacuating to exclude such objects such aswater, air and so on within the cracks from the interiors of the cracks.

The injection appliance for the repairing agent, which is employed inthe invention, is one in which the injection pressure is produced byutilization of the shape restoring force of the shape-memory alloy.

Many alloys indicating shape-memory effects are known. As representativealloys, there are a Ni-Ti alloy, a Cu-Al-Ni alloy, a Cu-Zn-Al alloy andthe like.

The shape memory effects are based on the thermoelasticity martensitictransformation. Normally, the shape memory effects are produced byrapid-cooling of these alloys from a range of the austenitic phase or βphase. Mechanical characteristics of the shape-memory alloy depend upontemperature, and change at the transformation temperature. Theshape-memory alloy is soft under a condition of a martensitic phase attemperature equal to or below the transformation temperature, while thestrength and hardness of the shape-memory alloy increase in the β phaseat temperature equal to or above the transformation temperature. Sincethe shape-memory alloy has such properties, a large restoring force isgenerated when deformation is applied to the shape-memory alloy underthe condition of the martensitic phase and heating causes theshape-memory alloy to be brought to the β phase to restore the shape ofthe shape-memory alloy. For example, the maximum restoring force reaches35 Kg/mm² for the Cu-Zn-Al alloy.

The shape restoring force is determined by the degree of deformation, aquantity of shape recovery, heating temperature and the like which aregiven to the martensitic phase. Considering the effects of temperature,the higher the treatment temperature above the transformationtemperature, the more the shape restoring force increases. Further,since the memory alloy per se has a predetermined or constant volume,some time is more or less required for reaching the ambient temperature.In either case, since the temperature does not rise instantly, the shaperestoring force gradually increases. In the case where the surroundingtemperature is constant, a generated force becomes a function of time.Furthermore, after the temperature has reached a predetermined value sothat the shape is restored, the restoring force is always maintained solong as the temperature is not lowered.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a force generating condition when a coil springmade of a shape-memory alloy is heated;

FIG. 2 is a view showing a relationship between the force generatingcondition and a varying condition of requisite injection pressure;

FIG. 3 is a view showing an example of an injection appliance used inthe invention, and is a cross-sectional view when a piston body iscontracted;

FIG. 4 is a view showing the example of the injection appliance used inthe invention, and is a cross-sectional view when the piston body isextended or lengthened;

FIG. 5 is a view showing another example of an injection appliance usedin the invention, and is a cross-sectional view of a condition in whicha container made of a shape-memory alloy is extended;

FIG. 6 is a view showing another example of the injection appliance usedin the invention, and is a cross-sectional view of a condition in whichthe container is deformed into a spiral form;

FIG. 7 is a view showing still another example of an injection applianceused in the invention, and is a cross-sectional view of a condition inwhich a coil spring is contracted;

FIG. 8 is a view showing the still another example of the injectionappliance used in the invention, and is a cross-sectional view of acondition in which the coil spring is extended;

FIG. 9 is a view showing an embodiment of a method according to theinvention, and is a flow chart of operation and procedure;

FIGS. 10(a) through 10(d) are views showing an embodiment of the methodaccording to the invention, and are views showing principal procedure inorder of operational steps;

FIGS. 11(a) and 11(b) are views showing another embodiment of the methodaccording to the invention, FIG. 11(a) being a view showing a conditionin which injection is practiced while drawing or suction is effected,and FIG. 11(b) being an enlarged view of a suction cylinder;

FIGS. 12 through 15 are views showing the conventional injectionappliances, respectively; and

FIG. 16 is a view showing a relationship between an injection pressuregenerating condition of the conventional appliance and a varyingcondition of requisite injection pressure.

PREFERRED EMBODIMENTS OF THE INVENTION

The principle of the invention will be described below with reference toFIGS. 1 and 2. An example of the force generating behavior of a shape-memory alloy is shown in FIG. 1, which shows a stress generating curveand a temperature change curve at the time a coil spring (transformationtemperature is about 0° C.) made of a shape-memory alloy of a copper,zinc and aluminum system (Zn: 20 wt %, and Al: 6 wt %) is cooled to -18°C. to be contracted, and is allowed to warm up naturally to the ambienttemperature (temperature is 15.5°) so that the coil spring is extended.The coil spring has its wire diameter of 3.5 mm, a coil outer diameterof 27.4 mm at contraction and 26.8 mm at extension, a length atcontraction of 31.2 mm at -18° C. and a free elongation length of 80.5mm at 15.5° C. (all of them are actually measured mean values). Fromthis figure, it will be seen that, in the force generating condition,the stress is initially 0 (zero), but gradually increases as thetemperature rises, and the stress is continuously maintained after thestress has reached maximum.

In the injection appliance in which the shape restoring force of theshape-memory alloy is utilized to inject the repairing agent, theabove-described disadvantages of the conventional appliances caneffectively be resolved. That is, in the case where the coil springhaving its characteristics illustrated in FIG. 1 is employed, thegenerating condition of the stress shows a tendency similar to achanging curve 21 of a requisite injection pressure shown in FIG. 16.Accordingly, when the shape-memory alloy, which generates the stress insuch a way, is utilized as a generating source of the injection stress,ideal injection can be practiced conveniently.

This will be further described with reference to FIG. 2. In FIG. 2,similarly to FIG. 16, the abscissa indicates "a lapse of time from thestart-up of injection or an injection length", while the ordinateindicates "the injection pressure of the appliance" and "the requisiteinjection pressure". The reference numeral 25 denotes a curve showing achanging condition of the injection pressure of an appliance whichemploys the coil spring made of the shape-memory alloy, and thereference numeral 21 denotes a straight line (identical with thestraight line 21 shown in FIG. 16) showing the changing condition of therequisite injection pressure. From this figure, it will be seen that thestraight line 21 showing a change in the requisite injection pressureand the stress generating rising curve 25 of the shape-memory alloy haveno substantial difference therebetween. Accordingly, there is almost nowaste in energy, and ideal complete injection can be realized.

In connection with the above, the change in the requisite injectionpressure is different from the straight line indicated by 21, forexample, in the case where the requisite injection pressure changesunder conditions indicated by the reference numerals 21' and 21" in FIG.2, complete injection can similarly be done. That is, in the case wherethe requisite injection pressure changes like 21', the injectionpressure of the coil spring has already reached the maximum requisitepressure at the time the maximum requisite pressure is required, and thepressure is maintained as it is. Thus, the requisite injection pressureand energy are naturally produced so that complete injection can bedone. Further, in the case where the requisite injection pressurechanges like 21", the injection pressure of the coil spring still doesnot reach the pressure at the point of time the maximum requisitepressure is required. When the predetermined time elapses, however, theinjection pressure of the coil spring reaches the maximum desiredpressure and, subsequently, the pressure is maintained as it is.Accordingly, only the point of time of completion of injection will moreor less be delayed, but there is no change in achievement of completeinjection.

Embodiments of the invention will be described below with reference tothe drawings.

First, with reference to FIGS. 3 through 8, injection appliances A, Band C will be described which are suitable in use in the methodaccording to the invention. The injection appliances A, B and C areconstructed such that each of them is provided with a driving sourcemade of a shape-memory alloy, and resin as a repairing agent is injectedinto cracks by a restoring elastic force of the driving source.

The injection appliance A schematically shown in FIGS. 3 and 4 isarranged such that a piston body (driving source) 31 made of ashape-memory alloy is mounted within a cylinder 30, and is extended whenthe piston body 31 is heated to temperature equal to or higher than thetransformation temperature. As illustrated in FIG. 3, after the pistonbody 31 has been cooled to temperature equal to lower than thetransformation temperature and has been contracted, the repairing agent,the resin 2, is filled within the cylinder 30. After an injection port32 at the forward end of the cylinder 30 is mounted to an injectionlocation, the piston body 31 is heated to temperature equal to or higherthan the transformation temperature. By doing so, as illustrated in FIG.4, the piston body 31 tends to be returned and extended to a conditionwhich is memorized by the piston body 30, whereby the resin 2 is pushedout and injected into the cracks. In this injection appliance, since thequantity of deformation of the piston body 31 is small, the quantity ofinjection is small. However, high injection pressure can be produced.

Next, the injection appliance B illustrated in FIGS. 5 and 6 is arrangedsuch that a container 40 in the form of a toothpaste tube is made of ashape-memory alloy, and is brought to a driving source in which, whenthe container 40 per se is heated to temperature equal to or higher thanthe transformation temperature, the container 40 is returned to acondition in which the container 40 is spirally wound. After thecontainer 40 has been cooled and extended and the resin 2 has filled inthe container 40, the forward end of the container 40 is mounted to theinjection location. Subsequently, the container 40 is heated, wherebythe container 40 i deformed into the memorized spiral configurationillustrated in FIG. 6, so that the resin 2 is squeezed out.

Further, the injection appliance C illustrated in FIGS. 7 and 8 isconstructed such that a coil spring (driving source) 51 made of ashape-memory alloy in which, when the coil spring 51 is heated, the coilspring 51 is lengthened and is returned to its memorized condition, isarranged within a cylinder 50 in the form a syringe. The arrangement issuch that, after the coil spring 51 has been cooled and contracted, theresin 2 is filled in the cylinder 50 as illustrated in FIG. 7, and whenthe coil spring 51 is heated, the coil spring 51 is extended as shown inFIG. 8 to push a piston 52 forwardly. In this connection, the referencenumeral 53 denotes an injection port provided at the front, end of thecylinder 50, and the reference numeral 54 denotes a back end cap.

In addition to the injection appliances, injection appliances havingvarious constructions can be considered. However, the injection pressureof these appliances which all utilize the shape restoring force of theshape-memory alloy varies in accordance with the curve as shown inFIG. 1. When the shape-memory alloy is heated to temperature equal to orhigher than the transformation temperature, the injection pressure ofthe resin 2 gradually increases. After the injection pressure hasreached the maximum injection pressure, the shape-memory alloy maintainsthat condition as it is, as far as the shape-memory alloy is not cooledto temperature equal to or lower than the transformation temperature.

In connection with the above, the transformation temperature of each ofthe driving sources in the above-described injection appliances A, B andC, that is, the piston body 31, the container 40 or the coil spring 51may optionally be set. If, however, the transformation temperature isset to one equal to or lower than the ordinary temperature, the shaperestoring force can naturally be produced only by natural heating due tothe atmospheric temperature and the injection pressure is maintained solong as cooling is not forced.

Operational procedure in the case where the injection appliance Cillustrated in FIGS. 7 and 8 is used to inject the resin into cracksoccurring in concrete to repair the cracks will be described withreference to FIGS. 9 and 10. In this case, the transformationtemperature of the coil spring 51 is set lower than the ambienttemperature. In this connection, 1 through 9 in the followingdescription correspond respectively to the marks 1 through 9 in the flowchart illustrated in FIG. 9.

1. First, as shown in FIG. 10(a), a cement water-damming agent and aseal material 60 of epoxy resin are used to seal surfaces of cracks.This is to prevent the injected resin from leaking out.

2. A drill is used from a location above the sealed cracks, to form abore 61 whose diameter is of the order of 10 mm and whose depth is ofthe order of 35 mm, for example, as illustrated in FIG. 10(b). Aplurality of bores 61, . . . may be formed in line. In this case, it ispreferable that intervals of these bores are made to be 20 mm through 25mm, for example.

3. An injection washer 62 is screwed into the bore 61 drilled asdescribed above, by the use of a screwdriver, and is mounted flush to awall surface. It is further preferable that an adhesive agent is appliedto the screw portion to screw the same into the wall surface.

4. The requisite quantity of resin 2 is filled into the cylinder 50 ofthe injection appliance c. As shown in FIG. 10(c), the injection port 53at the forward end of the cylinder 50 is screwed into the injectionwasher 62 and is mounted thereto.

5. The back end cap 54 of the cylinder 50 is removed. The coil spring 51made of the shape-memory alloy, which is beforehand cooled andcontracted, is mounted to a portion within the cylinder 50 which islocated in rear of the piston 52, as illustrated in FIG. 10(d), and theback end cap 54 is mounted to the cylinder 50 and is screwed therein. Bydoing so, when the coil spring 51 is heated naturally and itstemperature rises higher than the transformation temperature, the coilspring 51 tends to be returned to the memorized configuration, and isgradually extended or lengthened. By doing so, the piston 52 is pushedforwardly so that the resin 2 is injected into the cracks.

6. After the resin 2 within the cylinder 50 has been injected into thecracks, the cylinder 50 is left as it is for a predetermined period oftime. By doing so, the injection pressure of the coil spring 51 ismaintained so that the resin 2 reaches locations deep in the cracks.Subsequently, the cylinder 50 is removed or detached from the injectionwasher 62.

7. A suitable check valve is screwed into the injection washer 62 toprevent the resin 2 from flowing out of the cracks.

8. A repairing agent is immediately applied to the cracks from alocation above the injection washer 62 and is filled up in theneighborhood of the injection washer 62.

9. A surface of the concrete is finished.

On the basis of the above, one operation cycle has been completed.Subsequently:

10. The extended coil spring 51 is removed out of the interior of thecylinder 50.

11. The coil spring 51 is cooled to temperature equal to or lower thanthe transformation temperature by a suitable cooling machine.

12. Subsequently, the coil spring 51 is again contracted.

The contacted coil spring 51 is again mounted within the cylinder 50(step of the above 5). Hereafter, the above procedure is repeated overthe entire length of the cracks.

In connection with the above, in the case where sufficient injectionpressure cannot be produced in the step of 5, the coil spring 51 isremoved from the cylinder 50 (step 10). After the above-described steps11 and 12 are completed, the coil spring 51 is again mounted within thecylinder 50 and the injection should be repeated.

According to the above-described method, after the coil spring 51 hasbeen mounted to the location within the cylinder 50, the coil spring 51is naturally heated and is extended per se so that the resin 2 is pushedout. Accordingly, an operation relying upon man power is entirelyunnecessary or is entirely dispensed with. Thus, it is of course that anattempt can be made to save energy, and the injection pressure rises perse with lapse of time. Further, the injection pressure due to the coilspring 51 is maintained for a long period of time. Accordingly, it ispossible to practice ideal injection which is in accord with theinjection theory, making it possible to completely and reliably injectthe resin 2 into the cracks up to deep locations.

In connection with the above, the arrangement is such that thetransformation temperature of the coil spring 51 is brought to one lowerthan the ordinary temperature, and the coil spring 51 is returned to itsmemorized condition and is extended when the coil spring 51 is heatednaturally within the environment. However, the arrangement may be suchthat the transformation temperature is set to one above the ordinarytemperature, and a suitable heating source is used to forcibly heat thecoil spring 51. In that case, it is possible to freely control theinjection pressure by adjustment of the heating temperature. In thiscase, if the forcible heating is interrupted to naturally cool the coilspring 51 to room temperature, it is possible to easily contract thecoil spring 51. Accordingly, a cooling machine is dispensed with.

Next, an example of another repairing method, which employs theabove-described appliance c, will be described with reference to FIG.11. The method is arranged such that resin is injected into cracks whileair and water content existing within the cracks are eliminated. Themethod is one suitable in employment in the case where a plenty of airand water content exist within the cracks and have no refuge so thatsufficient resin cannot be injected into the cracks, if remainingintact. In this case, the cracks are first sealed gas-tightly, similarlyto the above-described method. At least two bores 70 and 71 are formedat predetermined intervals therebetween. As shown in FIG. 11(a), acylinder 50a having filled therein the resin 2 similarly to the above ismounted to one bore 70 of the adjacent two bores 70 and 71. An emptycylinder 50b is mounted to the other bore 71. As shown in FIG. 11(b),another cylinder 50c is connected, in a reverse manner, to the back endportion of the empty cylinder 50b. Coil springs 51a and 51b, which havebeen cooled and contacted, are mounted within the one cylinder 50a andthe another cylinder 50c which is connected to the back end portion ofthe another cylinder 50b.

By doing so, both the coil springs 51a and 51b are naturally heated andextended. As a result, the resin 2 is pushed into the cracks from theone cylinder 50a, similarly to the above-described case, while a piston52c within the another cylinder 50c connected to the back end portion ofthe another cylinder 50b is moved backwardly so that the interior of theanother cylinder 50c is reduced in pressure. Attendant on this, thepiston 52b within the cylinder 50b is also moved backwardly s that thecylinder 50b is reduced in pressure. By doing so, air and water contentexisting within the cracks are drawn into the cylinder 50b.

The resin 2 injected from the one cylinder 50a flows toward the othercylinder 50b through the cracks. Ultimately, the resin 2 enters thecylinder 50b. Thus, it is possible to confirm that the resin 2 iscompletely injected into the cracks between both the cylinders 50a and50b.

Subsequently, the one cylinder 50a is maintained as it is for apredetermined period of time, while the cylinder 50c connected to theback end portion of the another cylinder 50b is removed therefrom. Thewater content flowing into the interior is removed. Subsequently, theresin 2 is filled within the cylinder 50b. Another coil spring 51c (notshown) is mounted within the cylinder.

An empty cylinder is mounted to another bore (not shown) providedadjacent the bore 71, similarly to the above, and another empty cylinderis connected to the back end portion of the cylinder. Another coilspring, which has been contracted, is mounted within the cylinder. Atthis time, the resin 2 is injected into the cracks from the cylinder50b, while air and water content are removed from the cracks by thesecylinders.

The above-described procedure is repeated, whereby, in the case where aplenty of air and water content exist within the cracks so that there isno refuge, and in the case where the cracks are long in length, it ispossible to completely inject the resin into the cracks over theirentirety. The injection pressure of the resin into the cracks graduallyincreases from the point of time of injection start-up, entirelysimilarly to the above-described embodiments. After completion of theinjection, the large injection pressure can be maintained as it is.Accordingly, it is possible to completely practice injection of theresin into the cracks.

As described above in detail, the method according to the invention isarranged such that the driving source made of the shape-memory alloy isprovided and the injection appliance is used in which the shaperestoring force of the shape-memory alloy causes the repairing agent tobe injected into the cracks, whereby the injection pressure of therepairing agent into the cracks gradually increases, and the maximuminjection pressure is maintained for a predetermined period of time.Thus, superior advantages like ones listed below can be produced.

1. It is possible to reduce labor intensity of the injection operation.

The arrangement is such that the martensitic transformation temperatureof the driving source made of the shape-memory alloy is brought totemperature lower than the ordinary temperature, and the driving sourceis cooled to temperature equal to or lower than the transformationtemperature and is brought to a freely deformable condition, so that theinjection appliance is mounted to the cracks. The driving source isheated by air temperature and is returned to the memorized configurationnaturally. Attendant upon this, the injection pressure graduallyincreases per se and reaches the designed maximum pressure.Subsequently, the pressure is maintained. Accordingly, input operationssuch as manual input into the appliance as in the conventionalappliance, corrective work to tend to reduction of the injectionpressure, and so on are entirely dispensed with, so that the laborcontent of the injection operation is reduced.

2. It is possible to practice complete injection.

In the conventional method, there is a fear that, as injection proceeds,the injection pressure is attenuated as the repairing agent is pushedout of the injection appliance, it is impossible to retain the largeinjection pressure during injection final stage, so that the repairingagent is hardened while voids or cavities remain at the extremities ofthe cracks. In the invention, to the contrary, the pressure is not atall reduced even in the final injection stage, and the large injectionpressure can always be maintained. Thus, it is possible to practicecomplete injection.

3. It is possible to optionally set the injection pressure.

In the various conventional injection appliances, it is impossible toeasily alter the injection pressure. In the invention, however, since itis possible to adjust the mechanical characteristics of the drivingsource made of the shape-memory alloy, the injection pressure canoptionally be set. Further, the driving source can be used in exchangeto another driving source having different magnitudes of the shaperestoring force.

4. Evacuation is made from the interiors of cracks, to practice completeinjection.

In the case where air and water exist within the cracks so that there isno refuge therefrom, it is impossible to completely inject the repairingagent into the cracks completely. However, repair is made while theinteriors of cracks is being evacuated, whereby it is possible todischarge air and water within the cracks so that the repairing agentcan completely be injected to the extremities of cracks.

5. It is possible to improve the injection operational efficiency.

In the case where the conventional appliances is employed, it isrequired that an elastic spring is shortened or rubber is lengthened byman power. In the invention, to the contrary, only temperature iscontrolled to enable the shape restoring force of the driving source tobe produced. Further, only cooling of the driving source to temperatureequal to or lower than the transformation temperature enables thedriving source to be deformed freely and easily. Accordingly, it ispossible to reduce the labor of an operator and the energy consumptionto greatly improve the operational efficiency.

6. Safety is extremely high.

In the case where the conventional appliance is used, since it isrequired to extend or stretch and retract the elastic spring and rubberby man power, and since the pneumatic pressure and hydraulic pressureare employed, danger will be accompanied with accidental injuries or thelike. In the case of the invention, to the contrary, since the shaperestoring force cannot be generated unless the temperature varies, andsince the generating condition is also slow, there is totally no casewhere danger is exerted upon the operator even in the case where anappliance generating large injection pressure is used.

7. Injection under high pressure can easily be done.

Since man power input is not required, and since only control oftemperature enables high injection pressure to be produced, therepairing agent can be injected under high pressure without thenecessity of complicated devices, complex equipment and skilledmanpower.

We claim:
 1. A method of repairing cracks, wherein a repairing agent isforcibly injected into cracks occurring in an object to be repaired, themethod comprising the steps of:(a) gradually increasing injectionpressure of the repairing agent after start-up of injection of saidrepairing agent; and (b) maintaining said injection pressuresubstantially constant for a predetermined period of time, after saidinjection pressure has reached a predetermined pressure; wherein thegradual increasing of said injection pressure and the maintaining ofsaid predetermined pressure are achieved by a restoring force of ashape-memory alloy.
 2. The method of repairing cracks, according toclaim 1, wherein said shape-memory alloy, which was strained attemperature not more than a transformation temperature, is raised totemperature above the transformation temperature, thereby exhibitingsaid restoring force.
 3. The method of repairing cracks, according toclaim 2, wherein the transformation temperature of said shape-memoryalloy is not more than the ambient temperature, and wherein saidshape-memory alloy was strained at a temperature not higher than thetransformation temperature, is raised to a temperature by the ambienttemperature, thereby exhibiting the restoring force.
 4. The method ofrepairing cracks, according to claim 2, wherein said shape-memory alloy,which was strained at a temperature not higher than the transformationtemperature, is raised in temperature by an heating device, therebyexhibiting the restoring force.
 5. The method of repairing cracks,according to claim 2, wherein said shape-memory alloy is configured as acoil spring.
 6. The method of repairing cracks, according to claim 2,wherein said shape-memory alloy is configured as a container, andwherein said repairing agent is contained in said container.
 7. A methodof repairing cracks, wherein a repairing agent such as resin or the likeis forcibly injected into cracks occurring in an object, the methodcomprising the steps of:(a) gradually increasing injection pressure ofthe repairing agent after start-up of injection of said repairing agent;(b) maintaining said injection pressure substantially constant aftersaid injection pressure has reached predetermined pressure; wherein thegradual increasing of said injection pressure and the maintaining ofsaid predetermined pressure are achieved by a restoring force of ashape-memory alloy; and (c) evacuating said cracks simultaneously withinjection of said repairing agent, thereby discharging at least some ofthe substances existing within the cracks.